From 94b61705a911aebb090ff3e1a760ad4dbeecd0c6 Mon Sep 17 00:00:00 2001 From: Arslaan Pathan Date: Tue, 17 Mar 2026 21:43:31 +1300 Subject: A few things --- src/boot.s | 57 +++++++++++++++++++++++++++++ src/kernel.c | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 175 insertions(+) create mode 100644 src/boot.s create mode 100644 src/kernel.c (limited to 'src') diff --git a/src/boot.s b/src/boot.s new file mode 100644 index 0000000..592ba46 --- /dev/null +++ b/src/boot.s @@ -0,0 +1,57 @@ +/* Multiboot header dark magic, do not touch */ +.set ALIGN, 1<<0 +.set MEMINFO, 1<<1 +.set FLAGS, ALIGN | MEMINFO +.set MAGIC, 0x1BADB002 +.set CHECKSUM, -(MAGIC + FLAGS) + +.section .multiboot +.align 4 +.long MAGIC +.long FLAGS +.long CHECKSUM + +/* Multiboot does not define the esp/stack, create the stack ourselves */ +.section bss +/* Stack on x86 must be 16-byte aligned by the System V ABI standard */ +.align 16 +/* Create a symbol at the bottom, allocate 16KiB, then finally create a symbol at the top */ +stack_bottom: +.skip 16384 +stack_top: + +/* _start is the entrypoint */ +.section text +.global _start +.type _start, @function +_start: + /* we are in 32bit protected mode + interrupts disabled, paging disabled + kernel has full control over cpu */ + + /* setup the stack, point to the top becausei t grows downwrad on x86 for som e reason */ + mov $stack_top, %esp + + /* here we need to init crucial processor state. + load the gdt, enable pages, init isa extensions/floating point instructions and stuff + for now just dont do anything we'll add that later */ + + /* enter the high level kernel + ABI says we need 16-byte alignment here, we aligned that before and pushed a multiple of 16 bits (zero) so we fine + but i will realign for good measure anyway */ + .align 16 + call kernel_main + + /* if nothing left then just infinite loop */ + /* + 1. disable interrupts with cli/clear interrupts + 2. wait for next interrupt with hlt. because they disabled this will just lockup the ocmputer + 3. justincase it wakes up just jmp back to the hlt instruction + */ + cli +1: hlt + jmp 1b + +/* set the size of the _start symbol to the current location (.) minus it's _start +for debugging stuff */ +.size _start, . - _start diff --git a/src/kernel.c b/src/kernel.c new file mode 100644 index 0000000..eb5ac45 --- /dev/null +++ b/src/kernel.c @@ -0,0 +1,118 @@ +#include +#include +#include + +/* Check if the compiler thinks you are targeting the wrong operating system. */ +#if defined(__linux__) +#error "you are not using a cross-compiler, this is bad. use an elf cross-compiler for ix86 targets, for example, i686-elf-gcc" +#endif + +/* This operating system will only work for the 32-bit ix86 targets. */ +#if !defined(__i386__) +#error "This tutorial needs to be compiled with a ix86-elf compiler" +#endif + +/* Hardware text mode color constants. */ +enum vga_color { + VGA_COLOR_BLACK = 0, + VGA_COLOR_BLUE = 1, + VGA_COLOR_GREEN = 2, + VGA_COLOR_CYAN = 3, + VGA_COLOR_RED = 4, + VGA_COLOR_MAGENTA = 5, + VGA_COLOR_BROWN = 6, + VGA_COLOR_LIGHT_GREY = 7, + VGA_COLOR_DARK_GREY = 8, + VGA_COLOR_LIGHT_BLUE = 9, + VGA_COLOR_LIGHT_GREEN = 10, + VGA_COLOR_LIGHT_CYAN = 11, + VGA_COLOR_LIGHT_RED = 12, + VGA_COLOR_LIGHT_MAGENTA = 13, + VGA_COLOR_LIGHT_BROWN = 14, + VGA_COLOR_WHITE = 15, +}; + +static inline uint8_t vga_entry_color(enum vga_color fg, enum vga_color bg) +{ + return fg | bg << 4; +} + +static inline uint16_t vga_entry(unsigned char uc, uint8_t color) +{ + return (uint16_t) uc | (uint16_t) color << 8; +} + +size_t strlen(const char* str) +{ + size_t len = 0; + while (str[len]) + len++; + return len; +} + +#define VGA_WIDTH 80 +#define VGA_HEIGHT 25 +#define VGA_MEMORY 0xB8000 + +size_t terminal_row; +size_t terminal_column; +uint8_t terminal_color; +uint16_t* terminal_buffer = (uint16_t*)VGA_MEMORY; + +void terminal_initialize(void) +{ + terminal_row = 0; + terminal_column = 0; + terminal_color = vga_entry_color(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK); + + for (size_t y = 0; y < VGA_HEIGHT; y++) { + for (size_t x = 0; x < VGA_WIDTH; x++) { + const size_t index = y * VGA_WIDTH + x; + terminal_buffer[index] = vga_entry(' ', terminal_color); + } + } +} + +void terminal_setcolor(uint8_t color) +{ + terminal_color = color; +} + +void terminal_putentryat(char c, uint8_t color, size_t x, size_t y) +{ + const size_t index = y * VGA_WIDTH + x; + terminal_buffer[index] = vga_entry(c, color); +} + +void terminal_putchar(char c) +{ + terminal_putentryat(c, terminal_color, terminal_column, terminal_row); + if (++terminal_column == VGA_WIDTH) { + terminal_column = 0; + if (++terminal_row == VGA_HEIGHT) + terminal_row = 0; + } +} + +void terminal_write(const char* data, size_t size) +{ + for (size_t i = 0; i < size; i++) + terminal_putchar(data[i]); +} + +void terminal_writestring(const char* data) +{ + terminal_write(data, strlen(data)); +} + +void kernel_main(void) +{ + /* Initialize terminal interface */ + terminal_initialize(); + + terminal_writestring("Hello, kernel World!\n"); + + while (1) { + __asm__ __volatile__ ("hlt"); + } +} -- cgit v1.2.3